DE3784261T2 - DEVICE FOR PRODUCING AN IMAGE ON A PAPER SHEET. - Google Patents

Description

The present invention relates to an apparatus for producing an image on a paper sheet of the type described in EP-A-78,019, comprising a paper introduction section, a paper discharge section, a transport device for transporting the paper sheet along a paper transport path from the paper introduction section to the paper discharge section, and an electrophotographic device for transferring the image onto the paper sheet located in the paper transport path.

The apparatus of the type described above can be designed either for "face up" or "face down" feeding, with the surface of the paper sheet bearing the image facing upwards or downwards. The apparatus designed for face up feeding, as described for example in EP-A-78,019, reverses the page order of the sheets, whereas an apparatus designed for face down feeding is likely to cause the paper to curl as it is fed back on itself; therefore, due to an increase in the length of the paper transport path, there is an increase in the frequency of failures, making the transport device complicated and expensive and printing slow.

The invention therefore provides an apparatus for producing an image from an original on a paper sheet, comprising a paper introduction section, a paper discharge section, a transport device for transporting the paper sheet along a paper transport path from the paper introduction section to the paper discharge section, a sheet receiving device for receiving sheets from the paper discharge section, an electrophotographic device for transferring the image onto the sheet of paper located in the paper transport path, the paper introduction region and the paper discharge region being arranged on vertically opposite sides of the electrophotographic device, and with a storage device which supports the device and which is arranged below the paper transport path, the angle between the plane of the sheet of paper at any point on the paper transport path and its plane in the paper introduction region not exceeding 90º, the design of which is characterized in that a fed-through sheet of paper is discharged from the paper discharge region with the printed surface facing downwards, whereby when a stack of sheets located in the region on the sheet receiving device is turned over, the page order of the imaged surfaces of the sheets in the stack is the same as the page order of the corresponding copied originals.

The device can be designed as a table-top device.

In the preferred embodiment of the invention, the apparatus is less expensive to manufacture and is capable of printing on thick paper, envelopes and the like using only a face-down feeding mechanism without a face-up feeding mechanism and associated switching devices with reduced risk of failure.

The apparatus is preferably designed so that the quick print time (the period of time which begins at the time of issuing a print command and ends at the time after the complete output of a printed sheet of paper) is reduced by a large margin and the operability is improved.

It is further preferably designed to be inexpensive to manufacture, compact and lightweight. It is preferably designed so that troubleshooting can be carried out by even an inexperienced user in a natural posture without risk of soiling his hands or damaging the device. It is further preferably designed so that the user can reliably replace a cartridge used in the device in a natural posture, which is achieved by performing practically the same operation as troubleshooting from the front of the device from which paper is discharged in normal use.

The electrophotographic device preferably comprises a photosensitive member, an optical signal generator for irradiating the photosensitive member with a light pattern in accordance with the image to be produced, a developing device for developing a latent image on the photosensitive member and a transfer arrangement for transferring the developed image from the photosensitive member to the paper sheet. In addition, a fixing arrangement for fixing the transferred developed image on the paper sheet can be provided.

The optical output signal of the optical signal generator preferably impinges on the photosensitive element at an angle not exceeding 60º to a horizontal line passing through a central axis of the photosensitive element.

The development arrangement is preferably arranged above an optical signal incident part of the photosensitive element.

The electrophotographic device may comprise a charging arrangement for charging a portion of the photosensitive member and a cleaning arrangement for cleaning the photosensitive member of toner.

The transfer arrangement may be arranged on one side of the photosensitive element, the optical signal generator being arranged on the opposite side of the photosensitive element and the charging arrangement and the cleaning arrangement facing the bottom of the photosensitive element.

Furthermore, the transfer arrangement can be arranged above the bottom part of the photosensitive element.

The electrophotographic device may comprise a cassette provided with at least two of the parts comprising the photosensitive member, the cleaning assembly and the charging assembly.

The cassette can carry the transmission arrangement, which can be detached from the cassette.

The transfer assembly may be pivotally connected to the cassette at one end so that it can pivotally move about that end.

On the other hand, the opposite ends of the transmission arrangement can be pivotally connected to the cassette and supported by it.

The cleaning assembly may comprise a waste toner container, wherein it has a flat bottom surface or at least three projections defining a ground plane on its floor area and the centre of gravity of the cassette is in the ground plane.

The cartridge may be provided with a handle by which it can be held in the same position when it is inserted into and removed from the device and during transport. The cleaning arrangement can be held in the cartridge by means of the handle in such a way that a first straight line which intersects the handle and the center of gravity of the cartridge without the presence of used toner in the container is arranged in the region of a second straight line which intersects the handle and the center of gravity of the cartridge when there is a significant amount of toner in the container.

A paper guide device can be arranged above the photosensitive element and a paper discharge device can be arranged below the photosensitive element.

The device preferably has a housing, the lower front portion of which has a hopper part which is movable into and out of a position in which it receives printed sheets of paper.

The transfer device can be formed integrally with the cassette, thus eliminating the need to perform maintenance such as cleaning it; this also allows the transfer assembly to be easily moved away from the photosensitive member to facilitate, for example, the removal of jammed paper. This structure enables easy cleaning of the transfer assembly when trouble occurs.

If the development assembly is arranged above the photosensitive element contained in the cassette in order to electrophotographic device vertically, a movable part of the housing can be opened outwards from the front so that cassettes can be exchanged and jammed paper can be removed through the opening located between the stationary and the immovable part of the housing.

The invention is explained by way of example using the attached drawings. It shows:

Figure 1 is a partial view of an embodiment of a device according to the invention;

Figure 2 is a perspective view showing the external appearance of an embodiment of an apparatus according to the invention in which a discharge tray can be fitted to the outside of the apparatus housing;

Figure 3 shows an example of a device according to the invention, in which a laser diode is used as an optical signal generator;

Figure 4 shows an example of a device according to the invention in which a reflecting mirror is used in the optical path of the laser;

Figure 5 shows a movable part of an embodiment according to the invention in its open state and the direction in which a cassette is removed;

Figures 6(a) and 6(b) in combination show the manner in which the contact pressure exerted by the rollers of a fixing arrangement in an embodiment according to the invention is automatically released by opening the movable part;

Figures 7(a) and 7(b) in combination show the manner in which the degree of opening of the movable part in an embodiment according to the invention is limited to a predetermined angle by a stop element, and in which the opening angle is regulated even in the fully open position of the movable part so that the position of its centre of gravity is not shifted from the base of the device;

Figure 8 shows an embodiment according to the invention in which the fixing arrangement is provided on the immovable part ;

Figures 9(a) and 9(b) in combination show an embodiment of the invention in which a damping device is provided for preventing sudden opening of the movable part by gravity and in which the movable part is opened to such an extent that it comes into contact with the surface of the site on which the device is installed;

Figures 10(a₁), 10(a₂), 10(b₁), 10(b₂), 10(b₃) and 10(c₁), 10(c₂) show various examples of the design of a cassette of a device according to the invention;

Figure 11 shows an example of a cassette provided with lugs which can be used in a device according to the invention;

Figure 12 is a section showing the positional relationship between a handle and a cleaning arrangement provided on the cassette;

Figure 13 shows a known device in which paper is dispensed with the front side up; and

Figure 14 shows another known device in which paper is fed from its front side and discharged on the top side with its front side facing downwards.

The terms "right" and "left" used in the following description refer to the directions in the corresponding drawings.

Figure 13 shows a schematic structure of a known electrophotographic image forming apparatus. In the apparatus of Figure 13, a paper stacker 8 and a discharge tray 18 are arranged on the right and left sides, respectively, as viewed from the front of the apparatus. As viewed in Figure 13, a sheet of paper is fed from the right side, passed through the interior of the image forming apparatus, and discharged onto the tray 18 in such a way that an image formed on the surface of the sheet of paper faces upward. When the paper is discharged in this manner, it is the generally known "face-up discharge." In such a configuration, the width W of the image forming apparatus must be about three times the length l of the paper, while the depth D of the apparatus must be equal to the sum of the width w of the paper and an additional minimum length.

Figure 14 shows another known device in which paper is discharged in such a way that the image surface faces downwards. If the paper is discharged in this way, it is the generally known "discharge with the face down". If the discharge is done with the face down, the discharged paper sheets are stacked from the bottom to the top of the sheet stack in the order page 1, page 2, page 3, .... If the stack of discharged sheets is turned over with the face down so that the image surface of the top sheet is visible, the top sheet is page 1, while the following sheets are page 2, page 3, ...., so that it is not necessary to rearrange the stack of sheets in the page order. On the other hand, in the case of face-up discharge, when the stack of discharged sheets is brought into the state where the image area of the top sheet of the stack is visible, the top sheet is the end page and the bottom sheet is page 1, so that rearrangement of the stack of sheets in the page order is necessary.

In the known device according to Figure 14, the width W' of the image forming device is the same as the depth D of the device according to Figure 13, while the depth D' of the device according to Figure 14 is approximately equal to twice the length l of the paper.

Reference numerals in Figures 13 and 14 which are not listed above correspond to the reference numerals of identical parts in Figures 1 and 2, which are explained below.

The embodiment of Figure 14, which is for face-down discharge, has the disadvantages that there is an increase in paper curl because the paper is returned and that there is a greater frequency of failure due to an increase in the length of the paper transport path. In addition, since the paper transport mechanism is complicated, the production cost is higher, and there is also a considerable increase in the "first print time" (the period of time which begins at the time of issuing a print command and ends at the time of complete output of the first printed sheet of paper from the machine. The print quality can be judged by the length of the first print time).

In addition, unlike the face-up discharge, the face-down discharge requires a structure in which a paper transport path 21 is bent twice by about 90º in its course, so that it becomes impossible to prevent jamming or crumpling of thick paper, envelopes and the like.

In order to be able to print envelopes and the like without these problems, it is necessary to increase the radius of a circle defined by a bending part of the paper transport path 21 to about 5 cm, which leads to a considerable increase in the size of the device.

An apparatus capable of printing on envelopes and the like is provided with a mechanism in which a paper path switching lever is provided immediately behind a fixing device 11 so that paper is not bent but is discharged in the face-up discharge mode, thereby increasing the size of this type of apparatus and also the number of parts required, which in turn leads to an increase in production costs. In addition, it is necessary to switch between the face-up discharge mode and the face-down discharge mode as required; if the operator forgets to switch, jamming and associated machine failure may occur.

The state of the art is also plagued by the problem that used cassettes are complicated and difficult to replace and that the device can only be installed in a position that allows free access to the relevant side of the device that must be accessible for replacing parts; this requires an excessively large installation space. Since a tray system must also be provided to prevent jamming, a strong spring must be for lifting practically all the elements constituting a heavy electrophotographic system and an optical writing system, so that the apparatus frame must have great strength so as not to be deformed by the force of the strong spring, which leads to a further increase in production cost. In addition, in order to remove a cause of paper jamming, it is necessary to perform an operation in which the operator must bend down to look into the inside of the apparatus from an opening provided at a relatively low position and looking like an open fish's mouth, which is a troublesome operation. Furthermore, since the inside of the apparatus cannot be clearly seen, an essential element of the electrophotographic system may be damaged when the jammed paper is pulled out.

The structure and features of a device according to the invention are described below with reference to the accompanying drawings.

Figure 1 shows the structure of an embodiment of a device according to the invention.

A cylindrical photosensitive member or photosensitive drum 1 is rotatably mounted so that it can rotate in the direction of an arrow A. Around the photosensitive member 1 there are arranged a charging arrangement 2, an optical signal generator 3 for irradiating the photosensitive member with a light pattern in accordance with the image to be produced, a developing device 4 for developing a latent image on the photosensitive member 1, a transfer arrangement 5 for transferring the developed image from the photosensitive member 1 to the paper sheet, a cleaning arrangement 6 for cleaning the photosensitive member 1. element of toner and an erasing arrangement 7. Above the photosensitive element 1, a paper stacker 8, a paper guide roller 9 and paper alignment rollers 10 are arranged, while below the photosensitive element 1, a fixing arrangement 11 for fixing the transferred developed image on the paper sheet, a paper guide plate 12, discharge rollers 13, an exhaust fan 14 and a power source 15 are arranged. A control panel 16 is provided on the rear of the device body. The device has an outer casing 17.

A discharge tray 18 is arranged according to Figure 2 so that it can be pivoted in the direction of an arrow B about a pivot axis 18a in order to place it on the outside of the housing 17 when the device is not in operation.

The housing 17 has a paper insertion opening 19 in the region of its top and a paper discharge opening 20 in the region of its bottom and on its front. The paper feed roller 9, the paper alignment rollers 10 and the discharge rollers 13 form a transport device for transporting the paper sheet (not shown) along a paper transport path 21 from the paper insertion opening 19 to the paper discharge opening 20, while the parts 1 to 7 and 11 form an electrophotographic device for transferring the image onto the paper sheet located in the paper transport path 21. The housing 17 has a base part 17a which supports the device and is arranged below the paper transport path 21.

The image forming process carried out by the device according to the invention is explained below.

The photosensitive element 1 has a semiconductive surface layer with such a light characteristic that it has a relatively high electrical resistance in a dark place (ie the surface layer becomes an insulator), while when irradiated with light the electrical resistance of the irradiated part decreases (ie the irradiated part becomes an electrical conductor).

The charging arrangement 2 generates a corona discharge when a high voltage of several kilovolts is applied between a fine metal wire (not shown) and an earth electrode (not shown), so that a positive or negative electrical discharge is generated in its area.

The optical signal generator 3 is formed by an arrangement with a relatively short optical path, for example a liquid crystal aperture grid or an LED grid, and is used to convert electrical image information generated on the control panel 16 into optical signals (on and off signals in the form of light) and to output the converted signals. It should be noted that a laser sensor (not shown) can also be used as the optical signal generator 3, although the optical path becomes relatively long.

The ambient light is blocked by the outer casing 17, so that the photosensitive element 1 forms an insulator when the interior of the outer casing 17 is dark. In this state, when the photosensitive element 1 is rotated at a constant speed, the positive or negative electric charge generated by the charge arrangement 2 adheres to its surface (ie, the element 1 is electrically charged). The charged photosensitive element 1 is irradiated with light according to the image information from the optical signal generator 3. The irradiated part is therefore converted into an electric conductor, whereby the charge on the surface of the irradiated part is discharged to earth. Specifically, the surface of the photosensitive element 1 in this state has a part on which a charge corresponding to the image information is present and a part without a charge (ie a latent image is formed).

The developing assembly 4 contains toner (not shown) which is charged positively or negatively. The developing assembly 4 brings the toner into contact with the latent image via a developing sleeve 4a. Whether the toner is applied to a charged part of the surface of the photosensitive member 1 or the uncharged part depends on the polarity of the charge on the surface of the photosensitive member 1 and the polarity of the charged particles of the toner. Specifically, if the charge on the surface of the photosensitive member 1 is positive when the polarity of the charged particles of the toner is positive, the toner adheres to the uncharged part of the photosensitive member 1, while it adheres to the charged parts of the surface of the photosensitive member 1 when the polarity of the charged particles of the toner is negative. On the other hand, if the charge on the surface of the photosensitive member 1 is negative when the polarity of the charged particles of the toner is positive, the toner adheres to the charged part of the surface of the photosensitive member 1, while it adheres to the uncharged part of the surface of the photosensitive member 1 when the polarity of the charged particles of the toner is negative.

The top sheet of paper in the paper stacker 8 is guided to the paper alignment rollers by the action of the paper guide roller 9 and remains in this position in readiness.

The alignment rollers 10 rotate synchronously with the rotation of the photosensitive member 1, whereby the toner is Action of the developing arrangement 4 on its surface and the paper is advanced to an intermediate position between the photosensitive element 1 and the alignment rollers 10.

The transfer assembly 5 has two constituent elements, namely a fine metal wire (not shown) and a ground electrode (not shown), as is the case with the charging assembly 2. The transfer assembly serves to charge the back of the paper with positive or negative ions which are generated by the relatively high voltage applied between the two constituent elements. The toner developed on the surface of the photosensitive member 1 is attracted to the printing side of the paper by the positive or negative charge on the back of the paper, thereby effecting the transfer. The paper subjected to the transfer process is passed through the area between fixing rollers of the fixing assembly 11, whereby the toner is fixed on the surface of the paper. Instead of conventional fixing methods using heat and pressure rollers, a fixing method using a heated roller is used in the present embodiment in order to minimize the size of the apparatus. A heat source such as an infrared lamp is arranged at the center of a roller 11a, whereby temperature control is performed so that the surface temperature of the roller 11a is kept at a constant value. The surface temperature of the roller 11a depends on the type of toner used, but is generally in a range of about 140ºC to 200ºC. The toner on the paper comes into contact with the surface of the roller 11a and absorbs heat therefrom, so that resin contained in the toner as a component is melted and penetrates into the paper fibers. The melted toner is cooled and the surface of the paper as it is fed out of the area between the fixing rollers.

In this embodiment, the transfer assembly 5 is arranged on a horizontal line passing through the center of the photosensitive member 1 and on the front of the image forming apparatus. Thus, the transfer assembly 5 is arranged above the bottom part of the photosensitive member 1. The optical signal generator 3 is arranged on this horizontal line and on the rear of the apparatus. When the image forming apparatus is used for a long time, dust and toner accumulate inside the apparatus, and the amount of dust and toner accumulated is the largest in the center of gravity, i.e., the lower part of the apparatus. If toner or paper dust adheres to the transfer assembly 5, corona discharge cannot occur in the normal state when a high voltage is applied; in such a case, the transfer cannot be carried out satisfactorily. Toner or paper dust adhering to the optical signal generator blocks the passage of light and thus prevents the photosensitive element 1 from becoming electrically conductive, so that the charge on the surface is not sufficiently dissipated.

To solve these problems, the arrangement of the transmission arrangement 5 and the optical signal generator 3 in the lower part within the device is avoided.

If an optical system with a laser diode (not shown) is used as the optical signal generator 3, the length of the optical path l (Figure 3) must be at least about 300 mm, which means that reducing the depth D of the image forming apparatus according to Figure 3 is difficult. It should be noted that l is approximately equal to 300 mm in this embodiment. In order to minimize the depth D, a In the embodiment, an optical system using a laser diode having a reflecting part (or mirror 19b) as shown in Fig. 4 is provided, wherein a polygon scanner 19a rotating at a high speed must be arranged so that its longitudinal axis is horizontal, which means that a very heavy load is applied to a device for supporting the rotation of the polygon scanner 19a. This makes it difficult to ensure a long life. The light generated by the laser diode is reflected by the polygon scanner 19a rotating at a high speed and transfers the latent image to the photosensitive element 1 via the mirror 19b. In this embodiment, a liquid crystal aperture grid or an LED grid (the optical path of which is 70 mm or less) is used to form the optical signal generator 3, whereby the depth D of the image forming apparatus can be reduced. However, if a reflecting mirror is additionally provided, the optical signal generator 3 may also be formed by a laser scanner, but the cost is relatively high.

The paper passing through the fixing assembly 11 is led out of the image forming apparatus by the action of the feeding rollers 13. In this embodiment, the paper is fed out to the front of the apparatus in such a way that its printed surface faces downward. Furthermore, in this embodiment, the paper alignment rollers 10, which are defined by a pair of rollers, and the fixing assembly 11, which is also defined by a pair of rollers, are arranged such that the line intersecting the contact area between the former pair of rollers and the contact area between the latter pair of rollers (this line forms the paper transport path 21) is substantially vertical, and the photosensitive member 1 is arranged so as to be in contact with this vertical line in the transfer position.

After the transfer has been completed, a small amount of toner remains on the surface of the photosensitive element 1. This remaining toner is scraped off by the cleaning arrangement 6.

Furthermore, the surface of the photosensitive element 1 is uniformly irradiated by the erasing arrangement 7 in order to reliably discharge the charge from its surface and to make the surface state uniform.

The exhaust fan 14 is arranged in the area and below the fixing arrangement 11 in order to dissipate the heat generated by the voltage source 15 and the fixing arrangement 11.

The power source 15 supplies electrical power to all the units of the image forming apparatus. Since the power source 15 includes a transformer (not shown) and other heavy elements, it is located in the lowest part of the apparatus. In the case of an image forming apparatus with a relatively small floor area and a relatively high height, it is desirable to locate the power source 15 in the lowest part of the apparatus.

The control panel 16 serves to control a signal to be fed into the optical signal generator 3 and to connect the image forming device to a central computer (not shown) for sequential control of the elements of the device. Since the control panel 16 in this embodiment has a size which is approximately equal to the A4 paper format, it is arranged on the rear side of the image forming device.

With the above-mentioned contents, an image forming apparatus with a width W of 300 mm, a depth D of 170 mm and a height H of 260 mm is obtained. The height H is therefore greater than the depth D. The paper transport path 21 is not bent greatly, with the largest bend angle being about 20 to 30º, as described above. This makes it possible to print envelopes and the like without jamming and creasing. Investigations of a structure with a bend of the paper transport path 21 of about 90º have shown practically no problems.

However, if the belt transport path 21 is bent by 120º or more, problems such as jamming and creasing become significant for certain types of paper; if the bending angle exceeds 180º, a relatively large number of different envelope shapes will be creased almost every time they are printed.

The most preferred angle by which the paper transport path 21 can be bent is therefore a maximum of about 20º to 30º, while the preferred angle range is about 60º to about 80º.

If the apparatus is designed to maximize the deflection of the paper transport path 21 as described above and to discharge the paper with the top side facing downward, the paper transport path 21 may be substantially vertical as in the case of this embodiment, or it may be designed to have a structure such as that obtained by reversing the known design shown in Fig. 13 with the top side facing downward. In the latter case, problems arise such as an increase in the amount of toner adhering to the charging device 2 and the optical signal generator 3 due to gravity, a complication of the toner transport mechanism of the developing device 4, difficulties in using a sheet system suitable for reducing the size of the cleaning assembly 6, and damage to the image due to contact of the unfixed toner with the belt transport path 21 due to the fact that the printed surface of the paper is turned upward. In addition, the size of the apparatus is undesirably increased in the same way as in the prior art of Figure 13.

It is therefore preferable to realize a paper transport path 21 which is substantially vertical as in this embodiment, and it is very desirable to realize this structure to arrange the optical signal generator 3 so as to emit an optical signal to the center of the photosensitive element 1 from a position which is within a range of 60° around the horizontal line passing through the center of the photosensitive element 1. For the optical signal generator 3, it is preferable to emit an optical signal from a position which is substantially on this horizontal line. Furthermore, from the viewpoint of the structural features described above, it is very desirable to arrange the developing device 4 above the optical signal generator 3. It is preferable to arrange the developing device 4 within a range of 10° to 90° from this horizontal line. Specifically, it is preferable to arrange the developing sleeve 4a in the lowermost part of the developing device 4 in order to realize a structure that enables the most efficient transport of toner by gravity.

In an experimental run of this embodiment at a printing speed of 8 ppm, the fast printing time can be reduced to only 12 seconds, while the fast printing time in the known device according to Figure 14 is a relatively long paper transport path is generally 30 to 40 seconds.

In this embodiment, the photosensitive element 1, the charging arrangement 2 and the cleaning arrangement 6 are designed as a unit to form a cassette 22 which can be detached from the device body. Figure 5 shows the manner in which the cassette 22 can be inserted and removed when opening a movable part 23 of the image forming device. In Figure 5, the same elements as in Figure 1 are provided with the same reference numerals. The transfer arrangement 5 and the fixing arrangement 11 are rigidly attached to the inside of a movable part 23 and form the movable part 23 as a whole. The movable part 23 is supported by a pivot shaft 24 mounted on a stationary part 25 of the image forming device. When the cassette is to be removed, the movable part 23 is pivoted in the direction of an arrow C and the cassette 22 is removed in the direction of an arrow G, being guided and supported by a guide element (not shown) which is rigidly attached to the stationary part 25.

According to Figures 6(a) and 6(b), the fixing arrangement 11 is formed by two roller sections 31 and 32, which contain the rollers 11 and 11a and resilient elements, such as springs 34, which push the roller sections 31 and 32 away from each other and thus in the direction in which the contact pressure is released.

If the movable part 23 is opened, the contact pressure is therefore removed, while when the movable part 23 is closed, the roller section 32 is pressed against a stop element 33, whereby a normal contact pressure for fixing is realized.

If the movable part 23 is opened, the center of gravity is moved towards the front of the device; in the worst case, the device can fall onto its front. In the embodiment shown in Figures 7(a) and 7(b), however, a stop element 35 is provided so that the movable part 23 can only be opened to an angle of 0, whereby the position of the center of gravity is no longer in the bottom of the device, so that the device can be prevented from falling over.

If, for example, the fixing arrangement 11 is provided on the movable part 23, this becomes very heavy and if it is not opened carefully, in addition to hitting the stop element 35 and the bearing shaft 24, a detrimental impact can occur on the entire device. There is also a risk that the device will fall over or collide with another object. The occurrence of such accidents is prevented by the action of a damping device 36, which enables a smooth and slow opening of the movable part 23 at a predetermined speed.

It is also practically effective to arrange the fixing arrangement 11 as shown in Fig. 8 on the fixed part 25 in order to facilitate the removal of jamming due to paper passing through the fixing arrangement 11. As shown in Fig. 8, the movable part 23 is provided with one of the alignment rollers 10 and with paper guides 40. In such a case, it is necessary to design the apparatus so that the cassette 22 can be inserted or removed from the front of the apparatus without interference by the fixing arrangement 11. As shown particularly in Figs. 9(a), 9(b), in this design, the structure can be significantly simplified since no heavy element is provided on the movable part 23. It may therefore be possible to dispense with the stop element 35 and the damping device 36 and to allow such opening of the movable part 23 until it comes into contact with the surface of the place where the device is installed. The use of the damping device 36 naturally allows a smoother opening and closing of the movable part 23.

According to Figures 10(a) to 10(c2), the transfer assembly 5 can be provided on the cassette 22 and made detachable according to Figure 10(a2); the transfer assembly 5 can also be made pivotable about one or two regions in which it is supported by the cassette 22 according to Figures 10(b1) and 10(b2), thereby facilitating its cleaning and the removal of jammed paper. Figure 10(b3) shows how the lower end of the transfer assembly 5 can be received in a lock 5a of the cassette 22.

The cassette 22 may have a flat bottom surface or a plurality of lugs 41 to 44 provided on its bottom surface, as shown in Figure 11. Specifically, the cassette 22 may be designed to be supported by at least three lugs which together form a polygonal stable plane, the center of gravity of the cassette 22 being perpendicular to this plane. It is thereby possible to arrange the cassette 22 even on an uneven surface without the risk of unstable swinging of the cassette 22. The use of rubber leg members to form the aforementioned lugs improves stability and prevents the generation of noise. It is also possible to improve the degree of accuracy in assembling the cassette 22 by using the lugs as adjustment members when the cassette is inserted into the device body.

It should be noted that the position of the center of gravity of the cartridge changes with the amount of toner used; however, it is preferable that the above conditions regarding the center of gravity are met regardless of the amount of toner.

The cassette 22 can be inserted and removed using a handle 26 as shown in Figure 5. This handle 26 is formed by a member which is formed integrally with the casing of the cassette 22 so that it extends from the casing and in the direction of the axis of rotation of the photosensitive element 1. The handle 26 is provided in such a position that it is possible to pull the cassette 22 out of the image forming apparatus and to transfer it from one hand to the other without changing its position. When removing the cassette 22, the user opens the movable part 23, pulls the cassette 22 out in the direction of the arrow G and then transports it, for example, to another location. Since the handle 26 is located at the top of the cassette 22 when it is inserted into the apparatus body, it is evident that there is no danger that the attitude of the cassette 22 provided with such a handle 26 is changed during the removal process. During the removal process, therefore, the used toner accumulated in the cleaning device 6 arranged under the photosensitive drum 1 remains as it is, so that there is no danger that the used toner moves to one side and thereby runs out of the cassette 22. In addition, the cassette 22 according to this embodiment has a surface shaped and a center of gravity located so that it maintains the above-mentioned attitude without changes even if it remains outside the image forming apparatus for some reason.

Toner has a rest angle in the range of 40º to 50º with respect to the horizontal; if the inclination angle exceeds this range, the toner flows. Changes in the position of the cassette 22 during the removal process and transport or when temporarily remaining outside the image forming device should therefore remain in a range which is smaller than the above-mentioned rest angle. It is desirable that changes in the position of the cassette 22 are far smaller than the toner's rest angle. In order to achieve this, the cassette 22 according to this embodiment is designed as shown in the sectional view in Figure 12. If the cassette 22 has not yet been used, no used toner has yet accumulated in a used toner container 50 provided in the cleaning arrangement 6; the center of gravity of the cassette 22 is therefore at a point E, this point E and the handle 26 being connected by a straight line EH. When the cassette 22 is used, used toner accumulates in the used toner container 50, causing the center of gravity of the cassette 22 to move to a point F connected to the handle 26 by the straight line FH. However, the cleaning arrangement 6 is located at such a location that the straight lines EH and FH are adjacent to each other, thereby preventing undesirable inclination of the cassette 22 as far as possible during use.

As stated above, the image forming apparatus has a reduced floor area and therefore occupies a minimum area on a table. Specifically, the embodiment described above has a depth D of 170 mm, so that when the apparatus is placed on a normal table having a depth of 700 mm and A4 paper sheets are fed out from the front of the apparatus, the total of the paper length, ie 300 mm, and the depth of the apparatus, ie 170 mm, is 470 mm, thus providing a sufficiently large area on the table. remains. In addition, since the paper is fed out from the front of the machine, the operator can easily handle the paper sheets coming out of the machine. The design in which the paper is fed in from the top of the machine and fed out from the front enables the realization of a face-down discharge system with a paper transport path which is far simpler than in the prior art. Envelopes and the like can therefore be printed without an additional face-up discharge mechanism and associated switching devices and with significantly reduced problems such as jamming and wrinkling.

In addition, with this embodiment it is possible to shorten the quick printing time to 12 seconds for an A4 paper size, while with conventional 8 ppm devices it is 20 to 30 seconds.

The operator can easily replace cassettes and remove jammed paper in a natural posture, and can see his hand while doing this. There is therefore no risk of damaging an electrophotographic process element.

Since cassettes are replaced from the front of the device, no free space needs to be provided for this purpose as part of the installation space, which is the case with known devices where cassettes are replaced from a transverse side of the device.

In the embodiments of the invention described above, no shell system to prevent jamming with a strong spring for supporting a movable Partly with a weight of several tens of kilograms in the area of the bearing point and also no very solid frame can be provided to avoid deformation.

Furthermore, since the transfer assembly 5 is provided in the cassette 22, it is not necessary for the user to clean the transfer assembly (i.e., the transfer assembly is replaceable). The described embodiments of the invention enable easy cleaning of the transfer assembly in the event of abnormal operation occurring.

The user is able to easily insert and remove the cartridge using the handle, and it can be easily placed on a table or similar without accumulated used toner falling to one side.

Claims (18)

1. An apparatus for producing an image from an original on a paper sheet, comprising a paper introduction section (19), a paper discharge section (20), a transport device for transporting the paper sheet along a paper transport path (21) from the paper introduction section (19) to the paper discharge section (20), a sheet receiving device (18) for receiving sheets from the paper discharge section (20), an electrophotographic device (1-7, 11) for transferring the image to the paper sheet located in the paper transport path (21), the paper introduction section (19) and the paper discharge section (20) being arranged on vertically opposite sides of the electrophotographic device (1-7, 11), and a bearing device (17a) which supports the apparatus and which is arranged below the paper transport path (21), the angle between the plane of the paper sheet at any point on the paper transport path (21) and its plane in the paper introduction section (19) 90º, characterized in that the device is designed so that a paper sheet passed through is discharged from the paper discharge area (20) with the printed surface facing downwards, whereby when a stack of sheets which has formed during operation on the sheet receiving device (18) is turned over, the page order of the imaged surfaces of the sheets in the stack is the same as the page order of the corresponding copied originals. 2. Apparatus according to claim 1, characterized in that the electrophotographic device (1-7, 11) comprises a photosensitive element (1), an optical signal generator (3) for irradiating the photosensitive element (1) with a light pattern in accordance with the image to be produced, a developing device (4) for developing a latent image on the photosensitive element (1) and a transfer arrangement (5) for transferring the developed image from the photosensitive element (1) to the paper sheet. 3. Apparatus according to claim 2, characterized by a fixing arrangement (11) for fixing the transferred developed image on the paper sheet. 4. Device according to claim 2 or 3, characterized in that the optical output signal of the optical signal generator (3) impinges on the photosensitive element (1) at an angle not exceeding 60° with respect to a horizontal line passing through a central axis of the photosensitive element (1). 5. Device according to claims 2 to 4, characterized in that the development arrangement (4) is arranged above an optical signal incident part of the photosensitive element (1). 6. Apparatus according to claims 2 to 5, characterized in that the electrophotographic device (1-7, 11) comprises a charging arrangement (2) for charging a part of the photosensitive element (1) and a cleaning arrangement (6) for cleaning the photosensitive element (1) of toner. 7. Device according to claim 6, characterized in that the transfer arrangement (5) is arranged on one side of the photosensitive element (1), that the optical signal generator (3) is arranged on the opposite side of the photosensitive element (1), and that the charging arrangement (2) and the cleaning arrangement (6) face the bottom of the photosensitive element. 8. Device according to claims 2 to 7, characterized in that the transfer arrangement (5) is arranged above the bottom part of the photosensitive element (1). 9. Apparatus according to claim 6 or 7, characterized in that the electrophotographic device (1-7, 11) comprises a cassette (22) which is provided with at least two of the parts comprising the photosensitive element (1), the cleaning arrangement (6) and the charging arrangement (2). 10. Device according to claim 9, characterized in that the cassette (22) carries the transmission arrangement (5). 11. Device according to claim 10, characterized in that the transfer arrangement (5) is detachable from the cassette (22). 12. Device according to claim 10 or 11, characterized in that the transmission arrangement (5) is pivotally connected to the cassette (22) at one end so that it can be pivotally moved about this end. 13. Device according to claim 10 or 11, characterized in that the opposite ends of the transmission arrangement (5) are pivotally connected to the cassette (22) and are supported by it. 14. Device according to claim 6 or the claims dependent thereon, characterized in that the cleaning arrangement (6) has a container (50) for used toner, that the cleaning arrangement (6) has a flat bottom surface or at least three projections (41-44) defining a base plane on its bottom surface and that the center of gravity of the cassette (22) lies in the base plane. 15. Device according to claims 9 to 14, characterized in that the cassette (22) is provided with a handle (26) with which the cassette (22) can be held in the same position when it is inserted into and removed from the device and during transport. 16. Device according to claim 15, characterized in that the cleaning arrangement (6) can be held in the cassette (22) by means of the handle (26) in such a way that a first straight line (EH) which intersects the handle (26) and the center of gravity of the cassette (20) without the presence of used toner in the container (50) is arranged in the region of a second straight line (FH) which intersects the handle (26) and the center of gravity of the cassette (22) when there is a significant amount of toner in the container (50). 17. Device according to claims 2 to 16, characterized in that above the photosensitive element (1) a paper guide device (10) and below the photosensitive element (1) a paper delivery device (13) is arranged. 18. Device according to the preceding claims, characterized in that it has a housing (17) whose lower front section has a funnel part (18) which is movable into and out of a position in which it receives printed sheets of paper.